It has been found that substitution of up to 20 percent by weight of poly(ethylene terephthalate) (PET) for poly(1,4-butylene terephthalate) (PBT) in glass fiber reinforced, optionally impact modified, molding compositions improves the surface gloss of articles molded therefrom. Such compositions are described and claimed in Fox and Wambach, U.S. Pat. No. 3,953,394. Such a substitution, however, has a tendency to reduce notched Izod impact strength, flexural modulus, flexural strength and tensile strength. As a result, such glass reinforced PET/PBT blends find most advantageous use when improved surface gloss outweighs the reduction in physical properties. It has also been found that compositions with high heat distortion temperatures and resistance to warping during removal from the mold can be produced by reinforcing impact modified PBT with a combination of glass fiber and mica. Such compositions, which tend to have low surface gloss, are described and claimed in copending Liberti application, Ser. No. 925,992, filed July 19, 1978, now abandoned. German Offenlegungsschrift No. 2,931,430, July 31, 1980, based on U.S. Ser. No. 4,596, filed Jan. 18, 1979, now abandoned, describes PBT molding compositions, containing PET, impact modified with an acrylic resin and reinforced with glass fiber and mica. Such compositions are disclosed to have high impact strength and stiffness. The ratio of PBT to impact modifier is below 2:1, and the amount of PBT used with respect to PET is generally equal to or lower than 3:2. In addition, the ratio of combined polyesters to combined reinforcement is generally below 5:4, e.g., 4.5:4.
It has now been discovered that the addition of PET to the impact modified glass fiber and mica reinforced PBT compounds not only improves surface gloss but also it improves notched Izod impact strength, flexural modulus, flexural strength and tensile strength. Surprisingly, if the amount of impact modifier is controlled, based on the PBT content, to not less than 3 nor more than 4 parts by weight of PBT per part by weight of impact modifier, then very beneficial effects on heat distortion resistance can be obtained. Such a modification and the advantageous effects are nowhere suggested by the above-mentioned German Offenlegungsschrift. The above-mentioned patents, application and publication are incorporated herein by reference.